1. Field of the Invention
This invention generally relates to control systems for switch mode power supplies (SMPS), in particular digital control schemes.
2. Description of the Related Art
We have previously described in UK Patent Applications 0427893.3 and 0427894.1 both filed on 21 Dec. 2004, some improved control techniques for digital SMPS controllers.
Background prior art relating to PWM and PFM controllers can be found in US 2004/0037094 and in the datasheet on the Power Integrations (RTM) TOP242-250 TopSwitch GX family (®) datasheet. These latter devices typically run at a fixed frequency for medium to heavy loads, employing PWM as the control method, but switching to a lower frequency for light loads. It is also known to deploy a cycle skipping scheme where power cycles are skipped when an SMPS output voltage is above its target value (see, for example, the datasheet on the power integration (®), “TinySwitch” products TNY253/254/255).
Further background prior art can be found in US 2002/0057080, U.S. Pat. Nos. 6,275,018, 6,304,473, EP 0 874 446A, U.S. Pat. Nos. 5,757,625, 5,479,090.